Organization top to bottom and very KISS:
1. Headsets on my head
2. Sunglasses on my head, in my shirt pocket or (if polo shirt) dangling from "v" in shirt.
3. Pen in my shirt pocket or clipped in the "v" in my polo shirt. I haven't used a pencil since the second grade.
4. Timex's cheapest watch (with second hand) on my wrist.
5. Small lap pad strapped to my inboard leg (right or left seat). I will only use the lap desk for holding the flight plan and/or a Jepp plate for IFR. This is the small lap board that is basically 5.5 inches by 8 inches (or a half sheet of 8.5 x 11).
6. Penlight (two AA batteries) flashlight trapped under my left thigh (if night flying).
7. And this is the tough one to explain without pictures, but a sectional chart folded to what I call "two squares" and trapped between the inboard edge of the seat and whatever is in the middle (i.e in C152, wedged between seats, in a Piper warrior trapped between seat and the flap handle console).
To get the sectional to "two square". Take a brand new sectional and open it top to bottom (i.e. where the words North/South are printed, open it up once). Now, thumbing through the chart like you are looking for a known article in a magazine, find the area that you are going to be flying and open it like the spine on a book. You are now looking at "four" squares (i.e. there are two major fold lines and your chart opened like it is shows a NW, NE, SW and SE corner. Now, fold the map over so that you are looking at just "two squares" at a time. In the above it will show you just the NW and NE or the SW and SE by "flipping the chart". This two square size is perfect to squeeze between the seats and is easy to manage when you pull the sectional up to look at your check points. If you get real creative at your folding, you can make the chart "flippable" in either a North South direction or an East-West direction. Now you aren't fumbling with gigantic map syndrome. PS on my first solo, there were many times when I went IMC because of the gigantic chart blocking everything from view in a C-152.
That's it. There is nothing else you need that you can't pile on the seat next to you or in your flight bag just behind the opposing seat.
Now I have seen students come with every imaginable gadget there is. One guy brought a sort of tool caddy that had everything from calculators to needle nose pliers. Another guy found a medical supplier and got a pen that has a light on the end that hangs around your neck on a lanyard - it worked well for ten minutes until the plastic clip broke and his light/pen ended up in the cargo area of the 172. He borrowed my parker clip pen to finish that XC. One guy brought a "police special" maglight for a night flight - it took about half an hour for me to get my night vision back. Another guy showed up in a flight suit with all the pockets full of stuff - I'm sorry, if you were in the military or you are CAP, I'll let the flight suit go, but otherwise I'm embarrasing you out of this level of geekiness. The best one was the guy who brought his samsonite attache case and he opened it with all the pockets full and it had those foam separators and it made a little desk. I asked where exactly I was going to sit in this plan and he realized a little late that he couldn't "set up shop" on the seat next to him.
Have fun.